Mine is 10 and is obsessed with it! Almost to the extent of being a stalker. She knows everything about the big names and big name teams. We went to the WCWS this year as we were there for a tourney and she went to the games when her teammates went to a theme park! Love that kid!
My 15 yo watched a couple this year. She usually doesn't watch them on TV. She won't watch very much of a Braves game on TV, but she's the FIRST one in the family to start chopping when we go to a real game.
I often wonder if one of the differences between girls and boys is that boys (typically) will watch hours of baseball and Sportscenter while most girls do not. The boys will go out and imitate the baseball players swings (while picking up some good hitting mechanics along the way) while girls typically do not.
Boys are also playing baseball video games and are learning the rules and strategies of the game while most girls are not.
It's merely anecdotal on my part, it's just a theory.